Electrical pulse generating apparatus



June 17, 1969 1. E. LINKROUM ELECTRICAL PULSE GENERATING APPARATUS Filed April 10, 1967 INVENTOR. IRVING E. LINKROUH flaw; Mg

25 MICRO -SEC.

TQENE YS United States Patent 3 450,972 ELECTRICAL PULSE GENERATING APPARATUS Irving E. Linkroum, Hancock, N.Y., assignor to The Bendix Corporation, a corporation of Delaware Filed Apr. 10, 1967, Ser. No. 629,459 Int. Cl. H05b 3.7/02, 39/00, 41/14 US. Cl. 315-209 Claims ABSTRACT OF THE DISCLOSURE This invention relates to electrical apparatus and in particular to a spark generating system for providing a succession of spark gap discharge voltages.

An object of the invention is to provide an improved electrical system for generating spar-k discharges, such as an ignition system for combustion engines.

Another object of the invention is to provide a novel ignition circuit or the like which embodies only a small number of parts, requires only a small space for installation, has circuit protection for safety of components, and is reliable and efiicient in operation with low maintenance costs.

A further object of the invention is to provide novel apparatus which achieves more eflicient control and conductance of discharge gaps in spark generating systems useful as ignition systems for jet engines, gas turbine engines and the like.

The above and further objects and novel features. of the present invention will more fully appear from the following detailed description when the same is read in connection with the accompanying drawings. It is to be expressly understood, however, that the drawings are for purposes of illustration only, and are not intended as a definition of the limits of the invention.

FIG. 1 is a diagram illustrating one form of electrical circuit embodying the invention; and

FIGS. 2 and 3 are discharge current wave forms of storage and voltage multiplication capacitors, respectively, according to the invention.

The embodiment of the invention illustrated in the accompanying drawing is, by way of example, shown in the form of an apparatus or circuit adapted for use as an ignition system in combustion engines including jet and gas turbine type engines. The system shown is capable of producing high energy sparks at high efliciency with a low loss factor in the breakdown of individual components.

As shown in FIG. 1, one suitable embodiment of the invention comprises a source of electrical energy 101 connected to one side of a primary winding 11 of a powertype transformer 12, the other side of the primary winding being grounded. This transformer may be and preferably is of the high flux leakage or leakage reactance type. The secondary winding 13 has its external leads 14 and 15 connected respectively to terminal 150 of a diode 16 and to the common terminal 17 of a pair of relatively small series connected condensers 1 8 and 119. The other terminal of condenser 19 is grounded and the other ter- 3,450,972 Patented June 17, 1969 minal of condenser 18 is connected to the other terminal of diode 16. A second diode 21 is connected to terminal 15a and to ground through a resistor 22. The combination of the back-to-back connected diodes 16, 21 and condensers 18, 19 and the connections thereto constitute a voltage doubling circuit, the function thereof being well known in the electronic art. In essence, on alternate cycles, the capacitors charge up, through alternate diodes, to the peak transformer voltages produced across the secondary Winding 13. The voltages are series additive across capacitors 18, 19 to give twice the line voltage. It can be seen, for example, that when the supply voltage is of the order of v. A.C., transformer 12 may be suitably constructed to provide voltages across the respective con- .denser 18, 19 of the order of 1000 volts and hence, 2000 volts across these combined series additive capacitors. Between terminal 20 of condenser 18 and ground there is connected a damping resistor 23 in series with a relatively large storage condenser 24, one terminal of the resistor being connected to the terminal 20 and one terminal of condenser 24 being grounded. A resistor 26 connected between junction 25 and ground serves to slowly discharge condenser 24 when the system is out of operation.

A control spark gap 30, which includes a pair of spark ,gap electrodes 31 and 32, has its input electrode 31 connected to common terminal 25 and its output electrode 32 connected to terminal 33 of a high frequency, step-up pulse transformer 34. Transformer 34 comprises a primary winding 35 and a secondary winding 36, both windings having one extremity thereof commonly connected to terminal 33. A condenser 37 has one terminal thereof connected to electrode 31 of control gap 30, and its other terminal connected to pulse transformer primary winding 35, the condenser and winding being series connected in shunt across spark gap terminals 31, 32. The charging circuit for condenser 37 is completed by a resistance 38 connected between junction 33 and ground.

The ignition system as embodied in the diagram of FIG. 1 terminates in an igniter plug or discharge gap 40 which may, but need not necessarily, be of the so-called shunted surface type. The discharge gap has spaced electrodes 41 and 42, the former being connected to pulse transformer secondary winding 36 and the latter being grounded. A high resistive element 43 shunts the gap electrodes 41 and 42 to complete the discharge gap apparatus if it is of the low-voltage, shunted-surface type.

In operation, the storage condenser 24 is charged to the peak value of voltage appearing across condensers 1 8 and 19 in series additive relation. This same magnitude of voltage appears also on storage condenser 37, the resistance 38 being sufiiciently small in relation to condenser 37 to permit this. In one exemplary embodiment, the charging of capacitors 18, 19, 24 and 37 is done in incre- ;mental steps by source 10, 12 through diodes 16 and 21 until a peak voltage of the order of 2000 volts is stored on condensers 24 and 37. The charging circuit may be as disclosed in Loudon US. Patent No. 3,299,339. The voltage across condenser 37 is impressed across control gap terminals 31, 32, thereby causing ionization of the gap between said terminals. Upon ionization, the gap, which has been pre-set at a selected breakdown voltage, breaks down and condenser 37 discharges thereacross and through primary winding 35 of pulse transformer 34.

The surge of current through coil 35 induces a high voltage in secondary winding 36 of sufiicient magnitude to cause the discharge gap 40, across which this secondary voltage appears, to ionize and break down. Upon breakdown of gap 40, storage capacitors 18, 19, 24 and 37 will discharge through gaps 30 and 40 in series to generate a high energy ignition spark because of the large capacity of condenser 24 and large discharge current therefrom.

During the course of discharge by storage condenser 24, the same undergoes a well known oscillatory function, as shown by the voltage curve in FIG. 2. Condensers 18 and 19 would discharge in a similar manner except for the novel inclusion of resistance 23 in the circuit. It can be appreciated that the diodes 16 and 21 are uni-directional current devices which conduct current flow in one direction only to permit charging of the storage condensers by transformer 12 while preventing discharging thereof back through winding 13. However, during the oscillatory discharge of the condensers across gap 40, the polarity is such that during the negative voltage portions of the discharge cycle, the diodes 21 and 16 provide a conductive path from the grounded or normally low voltage sides of the condensers to the normally high voltages sides thereof. Thus, a condition exists which may impair and damage the diodes and their function or op eration and hence, the useful life thereof. To limit or obviate the inverse or negative discharge of the condensers through diodes 21 and 16, and hence a large current flow therethrough, current limiting resistance 22 and resistance 23 are inserted in the circuit.

While the storage capacitor 24 is discharging, the combined series condensers 18, 19 are also discharging through the circuit including igniter gap 40. To assure that there is no current reversal occurring during the discharge of these condensers, the time constant or product of the combined capacitance of series condensers 18, 19 and the resistance of resistor 23 through which they discharge should be about the same as or greater than the discharge cycle of storage condenser 24. As an example, where the oscillatory discharge cycle of condenser 24 is approximately 20 micro-sec., i.e., the time duration for the oscillations to be substantially dampened, then if a resistor 23 of 1000 ohms and a combined capacity of condensers 18, 19 equal to .025 microfarad is chosen, the resulting time constant will be as follows:

T=RC= 1000 x .025 x- T= .000025 or 25 micro-sec.

These discharges are graphically illustrated in FIGS. 2 and 3.

Thus, the charge on condensers 18, 19 remains positive with respect to diodes 16 and 21 and thereby prevents any reverse flow through the diodes from condenser 24.

Typical values of the various component parts which go to make up an operative circuit as shown in FIG. 1 for carrying out the invention are as follows:

Diodes 16 and 21 are Solitron Diodes, type IN2378 having a 3 kv. rating.

Multiplier capacitors 18, 19 are 0.05 microfarad rated at 1500 volts, or when series connected, equal to 0.025 microfarad.

Resistors 22, 23 are 1000 ohms, 3 watts.

Storage condenser 24 is 5.5 microfarads.

Trigger condenser 37 is 0.25 microfarad.

Resistor 38 is two 600 ohm resistances in parallel.

Although only a single embodiment of the invention has been illustrated in the accompanying drawing and described in the foregoing specification, it is to be expressly understood that the invention is not so limited, but may be embodied in other specifically different circuits. For example, other well known sources of interrupted, pulsating, direct or alternating current may be provided in lieu of the source shown, and other suitable types of rectifiers, pulse transformers, etc., known to the art may be utilized in lieu of the types illustrated and specifically mentioned. Additionally, the various parts of the circuit, particularly many of the parts which are series connected, may be rearranged with respect to each other without appreciably affecting the operation of the circuit.

Various other changes may also be made, such as in the electrical values suggested herein by way of example, without departing from the spirit and scope of the invention, as will now be understood by those skilled in the art.

What is claimed is:

1. Electrical apparatus comprising a source of electrical energy, a first relatively large storage condenser connected across said source to be charged thereby, a second relatively small storage condenser, a control gap having a predetermined breakdown voltage, a resistor, a transformer having primary and secondary windings, and a spark discharge gap, said control gap, secondary winding and discharge gap being connected in series in a discharge circuit across said first storage condenser, said second storage condenser being connected in series with said resistor across said source to be charged thereby simultaneously with said first storage condenser and being further connected in series with said primary winding across said control gap, whereby said second condenser when charged to said breakdown voltage discharges across the control gap through said primary winding, said discharge gap is ionized by the voltage thereby induced across the secondary winding, and the first storage condenser then discharges across the discharge gap, and said source comprising means for supplying alternating current electrical energy and a pair of condensers and a second resistor connected in series across said first condenser and across said discharge circuit.

2. Electrical apparatus as defined in claim 1 wherein the second resistor is of sufiicient ohmic value that during each oscillatory discharge cycle of the first storage condenser the discharge of said pair of condensers into said discharge circuit remains uni-directional.

3. In electrical apparatus a storage condenser system, a source of electrical energy connected to charge said system, a load circuit, and means for controlling the discharge of said condenser system into the load circuit, the condenser system comprising a circuit with a resistor, a first condenser, a second condenser and a third condenser, said first condenser, second condenser and resistor being connected in series across the third condenser and across said load circuit and said third condenser being connected directly across the load circuit.

4. Electrical apparatus as defined in claim 3 wherein the resistor is of sufiicient ohmic value that the duration of the initial uni-polarity discharge of said series connected first and second condensers through the resistor and the load circuit is of about the same duration as the duration of substantially the full oscillatory discharge of said third condenser through the load circuit.

5. Electrical apparatus as defined in claim 4 wherein said source is an alternating current source having one terminal thereof connected to the condenser system between and to the first sides of the first and second condensers and the other terminal thereof connected to the second sides of the first and second condensers through separate circuits containing reversely connected half-wave rectifiers.

6. Electrical apparatus comprising an alternating current source of electrical energy, a storage condenser, a discharge circuit connected across said storage condenser including means for controlling the discharging of the latter, and a voltage doubler charging circuit connected across said source and comprising a pair of condensers and a resistor connected in series across said storage condenser and across said dicharge circuit, a half-wave rectifier connected in series with each condenser of said pair across said source, said rectifiers being oppositely polarized with respect to said source whereby charges of like polarity are supplied to the condensers of said pair by said source.

7. Electrical apparatus as defined in claim 6 wherein said resistor is interposed between the high potential terminal of said pair of condensers and a terminal of said discharge circuit.

8. Electrical apparatus as defined in claim 6 wherein said resistor is of such ohmic value that the initial unipolarity discharge of said pair of condensers through said resistor and said discharge circuit is of about the same duration as substantially the full oscillatory discharge of said storage condenser through said discharge circuit.

9. Electrical apparatus as defined in claim 6 wherein the means for controlling the discharging of the storage condenser comprises a control spark gap.

10. Electrical apparatus as defined in claim 9 comprising a second storage condenser connected across said firstnamed storage condenser to be charged simultaneously therewith and connected in shunt with said control gap to trigger the same.

6 References Cited UNITED STATES PATENTS 2,799,809 7/ 1957 Lautenberger. 2,950,419 8/ 1960 Linkroum. 5 3,127,540 3/1964 Collins.

2,697,184 12/ 1954 Lautenberger.

FOREIGN PATENTS 929,070 6/1963 Great Britain. 10 672,173 10/ 1963 Canada.

JOHN W. HUCKE-RT, Primary Examiner. SIMON BRODER, Assistant Examiner.

15 US. Cl. X.R. 

